Qt5 attempts to match settings from current desktop environment.
qt5ct lets you set deskto-environment agnostic overrides.

Documentation

man qt5ct https://manpages.ubuntu.com/manpages/bionic/man1/qt5ct.1.html

repo https://sourceforge.net/projects/qt5ct/

Locations

/usr/share/qt5ct/qss/*.qss qss stylesheets referenced in UI

export QT_QPA_PLATFORMTHEME=qt5ct

`man qt5ct`	https://manpages.ubuntu.com/manpages/bionic/man1/qt5ct.1.html
repo	https://sourceforge.net/projects/qt5ct/